1. Field of the Invention
The present invention relates to an electric power steering apparatus equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit for controlling the driving of the electric motor.
2. Description of the Related Art
In the past, there has been known an electric power steering apparatus which is equipped with an electric motor for outputting assist torque to the steering wheel of a vehicle, and a control unit mounted on the electric motor for controlling the driving of the electric motor (see, for example, a first patent document (Japanese patent No. 3638269).
This electric power steering apparatus includes a power board on which a bridge circuit is mounted for switching the current of the electric motor, a control board on which a microcomputer is mounted for generating a drive signal to control the bridge circuit, and a high current board on which a conductive plate forming a high current wiring pattern is insert molded and on which a capacitor is mounted for absorbing current ripples, wherein the power board, the high current board and the control board are stacked or laminated one over another in this order so as to form a three-layer structure.
In the above-mentioned electric power steering apparatus, the control unit has a substrate comprising the three boards, i.e., the power board, the high current board and the control board, which are laminated one over another in this order to form the three-layer structure. Accordingly, the height of the control unit becomes large, and connecting members for connecting these boards with one another are required at the same time, resulting in increased connection or joint portions.
As a result, there arises a problem that the apparatus becomes large in size, high in cost, and low in reliability of electrical connections.